This invention relates to air heating devices which utilize the heat generated in a fireplace.
In the typical fireplace, most of the heat rises up and escapes through the chimney and relatively little heat is retrievable in usable form. The products of combustion are in part poisonous and are virtually impossible to separate from the heated air. Thus, safety factors dictate that the heated air be diverted up to the chimney with the products of combustion. As a result, there has long been sought a means for improving the heating efficiency of fireplaces while, at the same time, providing for adequate ventilation of the combustion products. A method of achieving this goal which has met with some degree of popularity is to conduct a quantity of air from a source external to the fireplace, such as the room, through one or more heat absorbing conduits in the fireplace. The air absorbs heat from the fireplace as it passes through the conduits and then flows into the room raising the temperature of the ambient air. The prior art shows several devices built in accordance with this principle. However, several problems have arisen with respect to these prior art devices. For example, in many such devices, the configuration of the air flow conduits is such that areas of stagnation develop within the conduits, thereby inhibiting the flow of air therethrough. Other prior art devices have the air flow conduits disposed beneath the fuel retaining grate so that heat absorption is by means of radiation alone, and not by a combination of radiation and conduction. In still other prior art devices, the arrangement of air flow conduits is such that the area of maximum heat concentration, i.e., the area of rising hot air immediately above the flame, is not utilized or is at best inadequately utilized for heating purposes.
An important consideration in fireplace design is to provide an adequate draft of air onto the fuel so as to facilitate both the initial ignition of the flame and the continued burning of the flame so as to consume the fuel as completely as possible without the need continually to restart the flame due to a tendency for the fire to suffocate from its own ashes. The prior art fireplace heaters do little or nothing to aid in providing such a draft and, in fact, their structure more likely has a tendency to inhibit the flow of air to the fuel. In those instances where the prior art does attempt to provide such draft, no means are provided for controlling the direction and volume of the flow of the draft so as to accommodate varying heating requirements and different kinds and amounts of fuel.